1. Field of the Invention
This invention is related to an electrocoating process and particularly to an improved electrocoating process that utilizes a novel electrocoating composition containing a cationic film-forming polymer.
2. Description of the Prior Art
Processes for electrocoating anionic carboxylic polymers are known as shown by Gilchrist U.S. Pat. No. 3,230,162, issued Jan. 18, 1966 and Gilchrist U.S. Pat. No. 3,362,899, issued Jan. 9, 1968. Also, processes for electrocoating cationic film-forming polymer are known as shown in Suematsu U.S. Pat. No. 3,755,093, issued Aug. 28, 1973; French Pat. No. 1,477,147, granted Mar. 6, 1967 and French Pat. No. 1,504,895, granted Oct. 30, 1967. But in these processes of electrocoating of anionic carboxylic polymers or cationic polymers, a problem arises in which an excess of neutralization agent accumulates as the polymers are deposited on articles being coated and the excess neutralization must be removed from the process.
An ultrafiltration step has been used to remove excess neutralization agent but this step requires additional equipment and adds to the costs of these processes. In other methods used to avoid the above problem, the cathode or the anode of the electrocoating cell used in these processes is flushed with water or a filtrate from the processes to remove excess neutralization agent but these methods also add to the cost and increase the complexity of the processes. Another technique used to avoid the above problem is to add replenishment compositions to these processes which are deficient in neutralization agent but dispersion of these replenishment compositions can be difficult and can cause problems.
In the novel process of this invention, the neutralization agent is deposited on the metal article being coated and does not need to be removed from the process and forms a corrosion retardant layer on the metal article being coated. Then a film-forming cationic polymer is electrocoated on the article and forms a coating on the article.